LIFE-Moms-Phoenix was a randomized clinical trial in overweight and obese pregnant women with the objective of testing the effects of an intensive lifestyle intervention on optimizing gestational weight gain, control of maternal hyperglycemia, and post-partum return to pre-pregnancy weight. The Phoenix center was conducted in collaboration between the Phoenix Indian Medical Center (PIMC) nurse midwifery and obstetrics services and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). It is part of the LIFE-Moms Consortium consisting of six other clinical centers that follow similar protocols and a research coordination unit. The study completed recruitment and follow-up of all women through delivery and 1 year after birth. Following this clinical trial, we are designing an observational study to evaluate, in women enrolled in pregnancy, the effects maternal, prenatal, and birth variables on the growth and health of the children of these pregnancies. We previously reported that the percent with excess GWG per week was significantly lower in the intervention group compared with the standard care group (61.8% vs. 75.0%; odds ratio 95% CI: 0.52 0.40 to 0.67). This modest beneficial effect was consistent across diverse intervention modalities in a large, racially and socioeconomically diverse US population of pregnant women. One-year post-partum anthropometric outcomes in mothers and children. Excess gestational weight gain (GWG) is a risk factor for maternal postpartum weight retention and excessive neonatal adiposity, especially in women with overweight or obesity. Whether lifestyle interventions to reduce excess GWG also reduce 12-month maternal postpartum weight retention and infant weight-for-length z score is unknown. Women (N=1150; 14.1 weeks gestational age at enrollment) with overweight or obesity were randomized to lifestyle intervention or standard care. Compared with standard care, lifestyle intervention reduced postpartum weight retention (2.27.0 vs. 0.76.2kg, respectively; difference of -1.6kg (95% CI -2.5, -0.7; p=0.0003); the intervention effect was mediated by reduction in excess GWG, which explained 22% of the effect on postpartum weight retention. Lifestyle intervention also significantly increased the odds (OR=1.68 (95% CI, 1.26, 2.24)) and percentage of mothers (48.2% vs. 36.2%) at or below baseline weight at 12 months postpartum (yes/no) compared with standard care. There was no statistically significant treatment group effect on infant anthropometric outcomes at 12 months. Compared with standard care, lifestyle interventions initiated in pregnancy and focused on healthy eating, increased physical activity, and other behavioral strategies resulted in significantly less weight retention but similar infant anthropometric outcomes at 12 months postpartum in a large, diverse US population of women with overweight and obesity.